Enone reductase enzymes of the Old Yellow Enzyme (OYE) family catalyze a range of reductions of α,β unsaturated ketones, aldehydes, esters, and nitriles that are of potential industrial importance. One reaction of interest is the hydrogenation of nitroalkenes, which is present in certain industrial explosives and serves as intermediates for the synthesis of a range of compounds, such as alkaloids, antibiotics, and biocides. Accumulation of the nitronate can be enhanced by a Y196F mutation of OYE (Meah and Massey, 2000, Proc Natl Acad Sci USA 97(20):10733-8; Meah et al., 2001, Proc Natl Acad Sci USA 98(15):8560-5), providing a attractive biocatalytic based production of a nitronate and a useful alternative to the more complex chemical transformation needed to provide the same products.
Another useful reaction carried out by enone reductases is the reduction of 3,5,5-trimethyl-2-cyclohexene-1,4-dione to produce (6R)-2,2,6-trimethylcyclohexane-1,4-dione, also known as levodione, which is a useful chiral building block for synthesis of naturally occurring optically active carotenoid compounds, such as xanthoxin and zeaxanthin. Old Yellow Enzymes OYE1, OYE2 and OYE3 from yeast Saccharomyces pastorianus and Saccharomyces cerevisiae can also catalyze stereoselective reduction of α,β-unsaturated carbonyls, esters and nitriles. However, these enzymes can have a narrow substrate recognition profile and/or have stability properties that are not suited for commercial applications. Thus, it is desirable to identify enone reductases having properties that may be advantageous, such as with respect to substrate recognition profile, stereoselectivity, and stability.